Memories are not sin, just, as, temptation to sin is not sin. Sin comes about when one gives into temptation, and given the opportunity, would act upon it.

As the Bible says of Jesus, " For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin. " (Hebrews 4:15)

God's children will retain their memories in the next life. The sinful part of their nature, however, will be done away with. We will be like Christ Jesus, in that, although He was tempted, He could not sin.